The new Queensferry Crossing will not open until between mid-July and the end of August, it has been revealed.
The opening has been delayed further due to “adverse weather conditions”.
Economy Secretary Keith Brown told MSPs that the bridge’s contractors had indicated that strong winds had affected the estimated completion date.
The bridge was originally due to open in December but bad weather had already delayed the completion date until May.
The £1.35bn link will replace the Forth Road Bridge as the main road route between Edinburgh and Fife.
Mr Brown gave the update to the Scottish Parliament’s rural economy and connectivity (REC) committee earlier.
The final section of the deck was lifted into place last month.
The contractor has reported there have been fewer clear weather windows than expected, particularly in relation to wind.
Marc Ellison, BBC data journalist
Planning a walking trip – let alone the construction of a bridge – is always challenging given Scotland’s notoriously fickle weather, which can be glorious one moment, tempestuous the next.
So it’s no surprise to see the extent to which winds have battered the Queensferry Crossing over the last few years.
Data obtained by the BBC from Transport Scotland reveals gusts between 30 and 127 miles per hour were recorded between September 2012 and May 2016.
A separate document indicated the safe working limits on the deck lifts and cabling were 25 and 28 miles per hour respectively.
And the data also shows certain months of the year are historically worse than others.
In an average December during this period, gusts of over 30 miles per hour were recorded by anemometers on 22 days; 18 days in your standard January, and 14 and 15 in a typical February and March.
The data also reveals that, on average, gusts of wind over 30 miles per hour were recorded for 40% of the days in 2013, 2014, and 2015.
The contractor, Forth Crossing Bridge Constructors, anticipated an average weather-related downtime of 20%.
Mr Brown said: “Today there are only nine weeks remaining to the end of May and the review has concluded that even with the best weather this date is not now safely achievable.
“I fully recognise the effort of the workforce in building this amazing new bridge. Over 13 million hours have gone into building the Queensferry Crossing over the past six years.
“There is no additional cost to the public purse and the Forth Road Bridge continues to carry traffic over the Forth during these final weeks of construction.
“While it’s clearly very disappointing the new bridge won’t be ready ahead of the contractual completion date, I believe it is important to take the time to make sure the bridge is built in the safest possible circumstances to the highest possible standards.”
Queensferry Crossing – fact and figures
The structure is 207m above high tide (683ft), equivalent to about 48 double decker buses stacked on top of each other.
It is 50m (25%) higher than the existing Forth Road Bridge
The steel required for the bridge deck weighs a total of 35,000 tonnes -equivalent to almost 200 Boeing 747s
The combined steel required for North and South viaducts weighs 7,000 tonnes – enough to make another 23 Kelpies.
The bridge has windshielding to almost entirely eliminate the need for closures during the frequent periods of high winds in the Forth estuary
Cables can be replaced with more ease than on the Forth Road Bridge – it can be done as part of normal maintenance works without closing the bridge.
Sally Cox, chairwoman of the board for the Forth Road Crossing Bridge Constructors (FCBC) said: “FCBC acknowledge that the uniqueness of this project and the onerous weather conditions it has experienced, particularly working at height crossing the Forth have created more challenges than we anticipated.
“FCBC have always been and remain ambitious about completing this challenging project at the earliest possible date and share Transport Scotland and the public’s frustration over this delay.
“We have assured Transport Scotland that every endeavour is and will continue to be made, to safely complete the project at the earliest opportunity.”